Piezoelectricity, Greek for "pressure" electricity, was discovered by the Curie brothers more than 100 years ago. They found that quartz changed its dimensions when subjected to an electrical field, and conversely, generated electrical charge when mechanically deformed. One of the first practical applications of piezoelectricity was in the 1920's by Langevin, who developed a quartz transmitter and receiver for underwater sound--the first SONAR. Before World War II, researchers discovered that certain ceramic materials could be made piezoelectric when subjected to a high polarizing voltage, a process analogous to magnetizing a ferrous material. In 1969, Kawai found very high piezo-activity in the polarized fluoropolymer, polyvinylidene fluoride (PVDF). While other materials, like nylon and polyvinyl chloride (PVC) exhibit the effect, none are as highly piezoelectric as PVDF and its copolymers. Like some other ferroelectric materials, PVDF is also highly pyroelectric, producing electrical charge in response to a change in temperature.
Transducer materials convert one form of energy into another, and are widely used in sensing applications. The tremendous growth in the use of microprocessors has propelled the demand for sensors in diverse applications. Piezoelectric polymer sensors are among the fastest growing technologies within the $18 billion worldwide sensor market. In the years since the discovery of piezoelectric polymer, the technology has matured, and numerous practical applications have emerged and been commercialized.
The reliability of conventional mechanical contact switches is reduced due to contaminates like moisture and dust which foul the contact points. Piezo film is a monolithic structure, thus is not susceptible to this failure mode. One demanding switch application is in a pinball machine that uses a piezo film switch constructed from a laminated piezo film on a spring steel beam, mounted as a cantilever to the end of a circuit board. In response to a direct contact force, the piezo film beam momentarily triggers a MOSFET. This provides a momentary "closure" for up to a 50 V maximum voltage. This piezo film switch does not exhibit the corrosion, pitting or bounce that are normally associated with contact switches, and has been tested in excess of 10 million cycles without failure.
However, all these prior art innovations still have not created a switch that is extremely small and simple. Switches in electronic applications are present in millions of applications, and the need for a small, low profile, low cost switch still exists, unfulfilled.